JP2007066770A - Static eliminator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a static eliminator having a simple circuit structure by constituting a high-voltage-side switch with a single switching element. <P>SOLUTION: This static eliminator is provided with an A.C. power source 1, transformers 32 and 42, voltage doubler rectifier circuits 3 and 4, a switch control circuit 8, a discharge electrode 7 and the like, where switches 2a and 2b and semiconductor switches Sa and Sb are arranged on the primary side and secondary side, respectively. Both the semiconductor switches Sa and Sb contain silicon carbide in a semiconductor constituent. It has a wide band gap as solid state property. Thereby, there is no need for transfer of charge caused on a P-N junction surface and it has a characteristic that a withstand voltage is high. When a switching element having such characteristics is used for a high-voltage-side switch, it is not necessary to arrange a plurality of switching elements in series with each another like a conventional product. That is to say, since a high voltage can be switched, only by a structure of a single switching element, a small number of components are required and contribute to miniaturization of a circuit. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a static eliminator that generates positive and negative ions.

Conventionally, there has been provided a static eliminator that discharges positively-charged ions and negative-polarity ions from a discharge electrode alternately and sprays these ions on the charge-eliminated object to be neutralized. ing.
An example of this type of static eliminator is disclosed in Patent Document 1. As shown in FIG. 4, this circuit supplies the output voltage from the power source 101 alternately to the positive and negative high voltage generation circuits 103 and 104 (a pair of high voltage generation circuits). A positive and negative high voltage from the voltage generation circuits 103 and 104 is applied to the discharge electrode 107.

  Specifically, the power supply 101 and both high voltage generation circuits 103 and 104 are connected via switches 102a and 102b (power supply switches). These switches 102a and 102b are alternately switched by a control signal from the switch control circuit 105. It is supposed to be turned on. Two resistors 106a and 106b (impedance elements) connected in series with each other are connected between the output terminals of the high voltage generation circuits 103 and 104, and the discharge electrode 107 is connected to the common connection point. It is said that. First, when the switch 102a is turned on by the switch control circuit 105, a positive high voltage is generated by charging the capacitor group 103a of the positive high voltage generation circuit 103. The output voltage is applied to the resistors 106 a and 106 b, and the shared voltage of the resistor 106 b connected to the negative high voltage generation circuit 104 is applied to the discharge electrode 107. In the discharge electrode 107, when the applied voltage reaches the discharge start voltage of corona discharge, corona discharge occurs and positive ions are generated.

  On the other hand, when the switch 102b is turned on, a negative high voltage is generated by charging the capacitor group 104a of the negative high voltage generation circuit 104a. Then, the output voltage is applied to the resistors 106 a and 106 b, and the shared voltage of the resistor 106 a connected to the positive high voltage generating circuit is applied to the discharge electrode 107. In the discharge electrode 107, when the applied voltage reaches the discharge start voltage of corona discharge, corona discharge occurs and negative ions are generated.

  In the above circuit configuration, only a voltage lower than the output voltage of the high voltage generation circuits 103 and 104 is applied to the discharge electrode 107. Therefore, in order to apply a voltage corresponding to the discharge start voltage to the discharge electrode, this discharge start A voltage higher than the voltage must be output. As a result, the output voltage of the high voltage generation circuits 103 and 104 must be increased unnecessarily.

In order to solve the above problem, the following proposal (Patent Document 2) has been made. As shown in FIG. 5, switches 6a and 6b are connected in parallel to resistance elements 5a and 5b connected between voltage doubler rectifier circuits 3 and 4, respectively, and switches 6a and 6b and voltage doubler rectifiers are connected. The switches 2 a and 2 b connected between the circuits 3 and 4 and the AC power source 1 are turned on / off by the switch control circuit 8. Specifically, the switches 2b and 6b are turned off when the switches 2a and 6a are turned on, and conversely, the switches 2b and 6b are turned on when the switches 2a and 6a are turned off. is there.
In such a configuration, when the switches 2a and 6a are turned on, the first and second capacitors 33 and 34 of the voltage doubler rectifier circuit 3 are charged, and a closed loop is formed by the second capacitor 34, the resistor 5b and the diode 45. It is formed. As a result, the charging voltage of the second capacitor 34 (that is, the output voltage of the voltage doubler rectifier circuit 3) is applied as it is to the resistance element 5b and eventually to the discharge electrode 7.

On the other hand, when the switches 2b and 6b are turned on, the first and second capacitors 43 and 44 of the voltage doubler rectifier circuit 4 are charged, and a closed loop is formed by the second capacitor 44, the resistor 5a and the diode 35. As a result, the charging voltage of the second capacitor 44 (that is, the output voltage of the voltage doubler rectifier circuit 4) is applied as it is to the resistance element 5a and thus to the discharge electrode 7. From the above, the output voltage of the high voltage generation circuit can be suppressed to the minimum necessary voltage value.
JP 2000-58290 A JP 2004-63431 A

However, in the above configuration, the switches 6a and 6b are arranged on the high voltage side in addition to the switches 2a and 2b on the low voltage side. However, when switching the circuit by switching, the switches 6a and 6b are arranged on the high voltage side. In addition, a very high voltage (several kV) is applied.
On the other hand, as a switch configuration, it is common to use semiconductor switching elements such as FETs (field effect transistors) that have good responsiveness and low power consumption. Therefore, in order to withstand a voltage of several k, it is necessary to arrange a plurality of switches in series as shown in FIG. 6 to suppress the voltage applied to one switch. In this respect, there is room for improvement. was there.
The present invention has been completed based on the above situation, and an object of the present invention is to provide a static eliminator having a simple circuit configuration in which a switch on a high voltage side is composed of one switching element.

  As a means for achieving the above object, the invention of claim 1 is characterized in that a positive polarity high voltage is generated by boosting a power source and a power source voltage applied from the power source and generating a positive high voltage at a first output terminal. A voltage generating means, a negative high voltage generating means for boosting a power supply voltage applied from the power supply and generating a negative high voltage at a second output terminal; and the power supply voltage generating the positive high voltage And a control means having a switching function for alternately supplying to the negative high voltage generating means, a discharge electrode, and the discharge electrode and the first and second output terminals, the discharge Switching means for selectively connecting an electrode to either the first output terminal or the second output terminal, between the first output terminal and ground, and between the second output terminal and ground Between each And when the control means generates a positive voltage in the positive high voltage generation means, the discharge means is connected to the first output terminal by the switch means. When the positive high voltage is applied to the electrode and the negative high voltage generating means is generating a negative voltage, the discharge electrode is connected to the second output terminal by the switch means. In the static eliminator for applying a negative high voltage to the capacitor, the switching means is characterized in that it is composed of one semiconductor switching element containing silicon carbide as a semiconductor component.

<Invention of Claim 1>
A semiconductor containing silicon carbide as a semiconductor component has a wide band gap as a physical property. For this reason, when a switching element such as an FET is formed of such a semiconductor, there is a characteristic that charge transfer hardly occurs at the PN junction surface and the withstand voltage is high. If a switching element having such characteristics is used as a switch on the high voltage side, it is not necessary to suppress a voltage applied to the switch by arranging a plurality of switching elements in series as in the prior art. That is, since the high voltage can be switched with the configuration of only one switching element, the number of parts can be reduced, contributing to the miniaturization of the circuit.

An embodiment of a static eliminator according to the present invention will be described with reference to FIGS. 1 and 2.
The AC power supply 1 has a voltage doubler rectifier circuit that outputs a high DC voltage (positive polarity) via a switch 2a having a contact (normally open and closed when a control signal is given). And a voltage doubler rectifier circuit that outputs a DC high voltage (negative polarity) through a switch 2b having an a contact (also referred to as negative polarity high voltage generation according to the present invention). 4 is connected.

  Transformers 32 and 42 are respectively provided between the input side of the double voltage rectifier circuits 3 and 4 and the AC power supply 1, and the secondary terminal of the transformer is connected to the double voltage rectifier circuits 3 and 4. The input terminals 31 and 41 are connected respectively. Therefore, for example, when the switch 2a is turned on and the power supply voltage is applied to the transformer 32, the voltage is boosted to a voltage multiplied by the turns ratio, and the secondary voltage V1 is applied to the input terminals 31a and 31b. The

Both voltage doubler rectifier circuits 3 and 4 are so-called Cockcroft-Walton type voltage doubler rectifier circuits.
The voltage doubler rectifier circuit 3 includes capacitors 33 and 34 and rectifying diodes 35a and 35b. When the secondary voltage V1 of the transformer 32 is applied to the input terminals 31a and 31b, the secondary voltage V1. Of the output side terminal 36a appears at a terminal 36a on one side of the output side terminal 36 with the polarity shown in the figure.
More specifically, when an AC voltage (secondary voltage V1) that causes the input terminal 31b to be positive is applied to the voltage doubler rectifier circuit 3, the rectifier diode 35b is energized, so that the capacitor 33 becomes 2 The battery is charged to the voltage level of the next voltage V1.

  After that, the polarity of the secondary voltage V1 is switched, and this time, when the voltage at which the input terminal 31a is positive is applied, the secondary side of the transformer 32 and the capacitor 33 are in series, Since the diode 35a is energized, the capacitor 34 is charged, and eventually reaches a voltage level twice that of the secondary voltage V1. As a result, a voltage twice as large as the secondary voltage V1 appears at the terminal 36a on one side of the output side terminal 36 with the polarity shown in the figure. The other output terminal 36b of the voltage doubler rectifier circuit 3 is connected to the ground.

  On the other hand, the basic configuration of the voltage doubler rectifier circuit 4 is the same as that of the voltage doubler rectifier circuit 3, and is configured with capacitors 43 and 44 and diodes 45 a and 45 b for rectification. A voltage twice as large as V1 appears at the terminal 46b on one side of the output side terminal 46 with the polarity shown in the figure. The other output terminal 46a of the voltage doubler rectifier circuit 4 is connected to the ground.

The output line L1 connected to the output terminal 36a of the double voltage rectifier circuit 3 and the output line L2 connected to the output terminal 36a of the double voltage rectifier circuit 4 are both combined into a common line and then connected to the discharge electrode 7. ing. The output line L1 connected to the output terminal 36a is provided with a semiconductor switch (corresponding to the switching means of the present invention) Sa.
The semiconductor switch Sa is a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor, details will be described later), the drain terminal D is connected to the discharge electrode 7, and the source terminal S is connected to the output terminal 36 a of the voltage doubler rectifier circuit 3. . A control signal from a switch control circuit 8 to be described later is input to the gate terminal G.

  On the other hand, the output line L2 connected to the output terminal 46b is also provided with a semiconductor switch (corresponding to the switching means of the present invention) Sb also made of MOSFET. Further, between these output lines L1 and L2 and at a position closer to the output terminals 36a and 46a than the switches Sa and Sb when viewed from the discharge electrode 7 side, there is a capacitor discharging resistor (corresponding to the impedance element of the present invention). ) R is connected.

The switch control circuit 8 outputs a pulse-like control signal that alternately repeats the high level “H” and the low level “L” to control the opening and closing of the switches 2a, 2b, Sa, and Sb. For example, when the output signal level of the switch control circuit 8 is “H”, the switches 2 a and Sa are turned off by inputting the “L” signal through the NOT circuit 9, while the switches 2 b and Sb are turned off. Is turned on when a "H" signal is input. On the other hand, when the signal is “L”, the on / off of the switches 2a, 2b, Sa, Sb is switched.
The switch control circuit 8 and the switches 2a and 2b correspond to the control means of the present invention.

Next, the circuit operation of the static eliminator will be described.
First, when the control signal output from the switch control circuit 8 is at "L" level, the switches 2a and Sa are turned on. Then, the first and second capacitors 33 and 34 of the voltage doubler rectifier circuit 3 are charged. Thereby, a charging voltage of the second capacitor 34, that is, a positive high voltage (for example, 2V1) appears at the output terminal 36a. At this time, since the output line L1 is in an energized state (switch Sa is closed), a positive high voltage is applied to the discharge electrode 7.

  Thereafter, when the control signal output from the switch control circuit 8 is switched from the “L” level to the “H” level, at this time, the switches 2a and Sa are turned off, and on the contrary, the switches 2b and Sb are turned on. . Immediately after this switching, the second capacitor 34 of the voltage doubler rectifier circuit 3 is in a state of accumulation of charge, but the charge is discharged through the resistor R, the diodes 45a and 45b, and the output terminal 46a. Thereafter, the first and second capacitors 43 and 44 of the voltage doubler rectifier circuit 4 are gradually charged. As a result, the charging voltage of the second capacitor 44, that is, a negative high voltage (for example, -2V1) appears at the output terminal 46b. At this time, since the output line L2 is in an energized state (switch Sb is closed), a negative high voltage is applied to the discharge electrode 7.

  Further, when the control signal output from the switch control circuit 8 is switched from the “H” level to the “L” level again from this state, at this time, the switches 2b and Sb are turned off. Sa turns on. Immediately after the switching, the second capacitor 44 of the voltage doubler rectifier circuit 4 is in a state where charges are accumulated, but the charges are discharged through the resistor R, the diodes 35a and 35b, and the output terminal 36b. Thereafter, the first and second capacitors 33 and 34 of the voltage doubler rectifier circuit 3 are charged again. Thereby, a charging voltage of the second capacitor 34, that is, a positive high voltage appears at the output terminal 36a.

  As described above, positive and negative high voltages are alternately applied to the discharge electrode 7, and ions are generated when the applied voltage reaches the discharge start voltage.

  The semiconductor switches Sa and Sb are provided in the secondary circuit of the transformers 32 and 33, and a very high voltage of several KV is applied at the time of opening and closing. In the case of the semiconductor switch Sa, the drain terminal D is connected to the discharge electrode 7, and the source terminal S is connected to the output terminal 36 a of the voltage doubler rectifier circuit 3. Therefore, for example, when the semiconductor switch Sa is opened from a state in which the switch Sa is in an on state (closed state) and a positive high voltage is applied to the discharge electrode 7, between the drain and source terminals. High voltage is generated.

  Therefore, in this embodiment, the semiconductor switches Sa and Sb are both formed from power MOSFETs (hereinafter simply referred to as FETs), but a silicon carbide semiconductor (SiC) is used as a semiconductor constituting the FETs. . Hereinafter, the configuration of the FET will be described.

  FIG. 2 schematically shows the structure (n channel) of the FET, and two n layers 81 and 85 are formed on the upper side of the p substrate 80. And the metal terminal 83 is provided in the n layer 81 on the left side shown in the figure, and the source terminal S is drawn out therefrom. On the other hand, the right side n layer 85 is also provided with a metal terminal 87 from which the drain terminal D is drawn. Further, the gate terminal G is drawn from the p substrate 80, and an insulating oxide film 91 is formed between the metal terminal 93 and the p substrate 80 where the gate terminal G continues.

  In this FET, two junctions of an n layer on the drain side-p substrate 80 and an n layer on the p substrate 80-source side, as shown in the figure, one is a forward diode and one is a reverse diode. Thus, when a voltage is applied between the source and the drain, an inflow of a current that tries to flow from the drain to the source is prevented. More specifically, current flow is prevented by a potential barrier generated at the PN junction surface on the diode side in the reverse direction. As described above, the breakdown voltage (Vdss) between the drain and the source of the FET is proportional to the height of the potential barrier, and a voltage exceeding the breakdown voltage is assumed between the two terminals (between the drain terminal D and the source terminal S). ), A breakdown phenomenon occurs and the function as a switch cannot be performed.

  In the present embodiment, the previous p substrate 80 is made of a silicon carbide semiconductor (SiC) made of a compound of carbon and silicon. The p substrate 80 is generally made of silicon (Si), but silicon carbide semiconductor (SiC) has a wide band gap as a physical property, and has a higher potential barrier at the PN junction than a silicon FET. . For this reason, there is a characteristic that charge transfer hardly occurs at the PN junction surface and the drain-source breakdown voltage (Vdss) is high. Specifically, the withstand voltage is about 10 kV, which is sufficiently higher than the maximum voltage (7 kV) expected to be applied between the drain and the source during opening and closing.

  As described above, in the present embodiment, switching elements having a sufficiently higher breakdown voltage than the maximum voltage expected to be applied between the drain and source at the time of opening and closing are used as the switches Sa and Sb on the high voltage side. There is no need to arrange a plurality of switching elements in series in consideration of the breakdown voltage. That is, since the high voltage can be switched with the configuration of only one switching element, the number of parts is reduced as compared with the conventional configuration, which contributes to the miniaturization of the circuit.

  Further, in the present embodiment, the output lines L1 and L2 are connected to the discharge electrode 7, respectively, and the semiconductor switches Sa and Sb are individually provided in the output lines L1 and L2, respectively. The resistors 5a and 5b are carried by one resistor R, and the circuit configuration is simply summarized.

<Other embodiments>
The present invention is not limited to the embodiments described with reference to the above description and drawings. For example, the following embodiments are also included in the technical scope of the present invention, and further, within the scope not departing from the gist of the invention other than the following. Various modifications can be made.

  (1) In this embodiment, the switches Sa and Sb on the high voltage side are constituted by power MOSFETs. However, this is applicable if the semiconductor component contains silicon carbide and has a high breakdown voltage. For example, a power transistor There is.

  (2) In the present embodiment, the capacitor discharge resistor R is connected between the output line L1 and the output line L2 in the circuit configuration of the static eliminator, but the circuit configuration as shown in FIG. 3, that is, the output line L1. The circuit operation (capacitor discharge) similar to that of the first embodiment can be performed even when the dedicated resistor R1 is provided between the output line L2 and the ground, and the dedicated resistor R2 is provided between the output line L2 and the ground. .

The circuit diagram of the static elimination apparatus which concerns on one Embodiment of this invention Schematic representation of power MOSFET structure The figure which shows another Example Figure showing a conventional example Figure showing a conventional example The figure which shows the state which arranged the switch in series

Explanation of symbols

1 ... AC power supply 3, 4 ... Voltage doubler rectifier circuit (positive high voltage generating means, negative high voltage generating means)
7 ... discharge electrode 8 ... switch control circuit (control means)
R: Resistance (impedance element)
Sa, Sb ... Semiconductor switch (switching means)

Claims (1)

Power supply,
A positive high voltage generating means for boosting a power supply voltage applied from the power source and generating a positive high voltage at a first output terminal;
A negative high voltage generating means for boosting a power supply voltage applied from the power supply and generating a negative high voltage at the second output terminal;
Control means having a switching function for alternately supplying the power supply voltage to the positive polarity high voltage generation means and the negative polarity high voltage generation means;
A discharge electrode;
It is interposed between the discharge electrode and the first and second output terminals, and selectively connects the discharge electrode to either the first output terminal or the second output terminal. Switching means for causing
An impedance element interposed between the first output terminal and the ground, and between the second output terminal and the ground, respectively.
When the control means is generating a positive voltage in the positive high voltage generating means, a positive high voltage is applied to the discharge electrode by connecting the discharge electrode to the first output terminal by the switch means. And apply
A neutralization device that applies a negative high voltage to the discharge electrode by connecting the discharge electrode to the second output terminal by the switch means when the negative high voltage generating means is generating a negative voltage. In
The static eliminator is characterized in that the switching means is constituted by a single semiconductor switching element containing silicon carbide as a semiconductor component.

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